1. Field of the Invention
The present invention relates to a scanner system and, more particularly, to a scanner system having a function of, using a computer, correcting any color misregistration generated in reading a color image by a scanner.
2. Description of the Related Art
Generally, a linear sensor is used as the image sensing device of a scanner for reading a color image.
In this case, two systems are available to convert the read image into a color image, e.g., to separate the image into three primary colors (R, G, and B), i.e., red, green, and blue components: a system which separates the light source into three primary colors and scans the image three times ("three-pass system") and a system which scans the original only once using a color CCD linear sensor which has a plurality of arrays of charge-coupled devices (CCDs) with three primary color filters formed thereon ("one-pass system").
In the RGB system, as the linear sensor used for the latter one-pass system, a "two-line linear sensor" having a total of two arrays of CCDs, i.e., an array of green CCDs and an array of red/blue CCDs, or a "three-line linear sensor" having three arrays of CCDs for red, green, and blue can be used.
FIGS. 14A to 14C are schematic views showing conventional linear sensors.
FIGS. 14A and 14B respectively show a two-line linear sensor and a three-line linear sensor.
R, G, and B in these drawings represent pixels of red, green, and blue CCDs, respectively, which are aligned in the main scanning direction (longitudinal direction) of the sensor.
The three-line linear sensor shown in FIG. 14B prepares data of one pixel of an image on the basis of outputs from the G, B, and R pixels aligned in the horizontal direction.
The two-line linear sensor shown in FIG. 14A prepares data of one pixel of an image on the basis of outputs from the G, B, and R pixels adjacent to each other. However, since the number of B or R pixels is 1/2 that of G pixels, B and R data are used twice to prepare image data.
When an original is sensed by a so-called "one-pass system" using a sensor having a plurality of lines in the main scanning direction, a color misregistration inevitably occurs because of its principle.
This is because the R, G, and B values constituting one pixel of the sensed image are obtained by sensing the original at positions slightly shifted from each other.
To cope with this problem, the conventional scanner temporarily stores a sensed image signal and reads the signal from a buffer incorporated in the scanner main body at a timing at which such color misregistration may not occur.
In some cases, the buffer is incorporated not in the scanner main body but in the linear sensor, and such a buffer incorporated type linear sensor as shown in FIG. 14C is used. With this arrangement, the entire scanner apparatus can be easily controlled.
As described above, the conventional scanner uses a buffer incorporated type linear sensor as shown in FIG. 14C to temporarily store a sensed image signal in the buffer and reads out the signal from the buffer at a predetermined timing, thereby preventing a color misregistration.
Such a buffer is sometimes separately arranged in the scanner main body, instead of in the linear sensor.
However, when the buffer is arranged in the scanner main body, the scanner becomes bulky, and the apparatus becomes expensive accordingly.
In case of the buffer incorporated type linear sensor as well, a sub-scanning direction in which color misregistration correction can be performed is limited to only one direction. When a sub-scanning operation is performed in the opposite direction, the color misregistration undesirably increases. Therefore, a bidirectional sub-scanning operation cannot be performed though it is convenient in practice.
When an original is to be read with various resolutions, the degree of color misregistration changes depending on the read resolution. When a buffer is used to shift the timing of outputting the image signal, the color misregistration undesirably increases.